Laser-to-fiber coupling

ABSTRACT

Our wafer scale processing techniques produce chip-laser-diodes with a diffraction grating ( 78 ) that redirects output light out the top ( 88 ) and/or bottom surfaces. Generally, a diffraction grating ( 78 ) and integrated lens-grating ( 78 ) are used herein to couple light from the chip to an output fiber ( 74 ), and the lens-grating ( 78 ) is spaced from the diffraction grating ( 76 ). Preferably the diffraction grating ( 76 ) and integrated lens grating ( 78 ) are also used to couple light from the output fiber ( 74 ) back to the active region of the chip. The integrated lens-grating ( 78 ) can be in a coupling block ( 82 ). The use of a coupling block ( 82 ) can eliminate “facet-type damage”. A coupling block ( 82 ) is generally used herein to couple light from the chip to an output fiber ( 74 ), and preferably to couple feedback reflected from the fiber ( 74 ) back to the chip.

TECHNICAL FIELD

[0001] These are improved devices and/or methods of makingelectrically-pumped chip-laser-diodes that arehorizontal-light-generating but surface-emitting. The diodes are laserchips manufactured using semiconductor wafer processing techniques.

BACKGROUND

[0002] A major source of interest has been to reduce the cost andcomplication of the assembly of electro-optic devices through thecoupling of the light into an external waveguide or other media. Thedesire to effectively couple light has lead to the development ofvertically-emitting (surface-coupled) diodes (as opposed toedge-emitting diodes). The term “vertical” is used in the industrygenerally for any light output through the top and/or bottom surfaces,including, for example, light coming out at 45 degrees from thevertical. While these chips generate light horizontally (parallel to thetop surface), they use gratings to change the direction of the light andcouple light out top and/or bottom surfaces. The term “light” as usedherein, includes not only visible light, but also infrared andultraviolet. The term “laser” is used herein to describe lightgenerating devices having an electrically or optically pumpedactive-region, including devices using two reflectors that form ends ofan optical cavity and optical devices that accept a light waveform inputand have an amplified light waveform as an output. Lasers generallyamplify the light that is allowed to resonate in the cavity. The term“diode” is generally used herein to mean an electrically-pumped, laserchip.

[0003] In addition to the horizontal-cavity edge-emitting type of laser,there are vertical-cavity, vertically-emitting laser chips, i.e., thevertical-cavity surface emitting laser, or VCSEL. VCSELs, however, havehad substantially reduced performance and a complicated device structurethat does not effectively translate across the different materialsystems (such as GaAs to InP) for low cost manufacturing. The gainvolume for VCSEL is very small and thus the output power is low. Notethat VCSELs, like edge-emitters, bring light directly out, withoutdiffracting the light.

[0004] The need for better vertically-emitting structures has driven theindustry to examine a wide number of methods to couple light verticallyout of a horizontal cavity structure. Proposed structures include theuse of gratings (see, e.g., U.S. Pat. No. 6,219,369 to Portnoi, et al.,which uses a single diode on a chip and U.S. Pat. No. 5,673,284 toCongdon, et al., which uses four stripe diodes on a chip). The classicapproach to grating coupled devices is to utilize a surface blazedgrating with fingers extending down into the surface of a cladding overthe passive region to couple light from an active region (containing,e.g., a quantum well, a p-n homojunction or a double heterostructure)through the passive region, and then vertically out of the device. Atypical such vertically-emitting laser might have an active region about10 microns wide by 500 microns long, and two Bragg gratings as end-ofcavity-reflectors, and an output grating designed both to couple lightout and to reflect light to the active region as the feedback (generallyabout 70-90% coupled out and 10-30% fed back to give the desirednarrow-band emission).

SUMMARY OF THE INVENTION

[0005] Our wafer scale processing techniques produce chip-laser-diodeswith a diffraction grating that redirects output light out the topand/or bottom surfaces. Noise reflections are preferably carefullycontrolled, allowing significant reduction of the signal fed to theactive region. Combination gratings and additional gratings and/orintegrated lenses on the top or bottom of the diode can also be madeutilizing wafer scale processes, reducing or even eliminating the needfor the expensive discrete optical elements traditionally required tocouple light out (e.g., into an optical fiber) and reducing alignmentproblems (prior art packaging of a diode has required tedious manualpositioning of discrete optics). The diffraction grating can redirect anovel feedback from the optical output (e.g., fiber) to produce lasingthat aligns itself to the fiber input, and such self-aligned lasingfurther reduces assembly costs.

[0006] Generally, a diffraction grating and integrated lens-grating areused herein to couple light from the chip to an output fiber, and thelens-grating is spaced from the diffraction grating. Preferably thediffraction grating and integrated lens grating are also used to couplelight from the output fiber back to the active region of the chip. Theintegrated lens-grating can be in a coupling block. The use of acoupling block can eliminate all solid-to-air interfaces in couplinglight between the chip and a fiber.

[0007] This can be an improved method of horizontally generating lightwithin a semiconductor structure, and diffracting at least a portion ofthe generated light out of the structure and into an optical fiber, themethod comprising providing a semiconductor substrate having a substratewith a bottom surface and having a lower metal contact on at least aportion of the substrate bottom surface; providing a core layercontaining active-region, a waveguide region longitudinally-displacedfrom an active and a passive region with an adjacent passive-end facet,the core layer being over the substrate; providing an top cladding layeron the core layer; providing a top electrode layer over the top claddinglayer; providing a top metal contact on a portion of the top electrodelayer over the active region; providing grating fingers extending downinto the top cladding layer over at least a portion of the waveguideregion to provide a diffraction grating; providing an integratedlens-grating wherein the lens-grating is spaced by at least one-hundredwavelengths from the top grating from the diffraction grating; providingan optical fiber; and applying a voltage between the top and bottommetal contacts, whereby light is generated in the active region and atleast a portion of the generated light is diffracted out of at least oneof the cladding upper surface and the substrate bottom surface, andfocused into the fiber by the lens-grating. In some embodiments thelens-grating is on the substrate bottom.

[0008] In some embodiments a coupling block with the optical fiberattached, is connected to the chip. In some embodiments the lens-gratingis in the coupling-block. In some embodiments the diffraction gratingand integrated lens-grating are also used to couple light from theoutput fiber back to the active region of the chip. In some embodimentsan upper buffer layer is provided between the top cladding layer and thecore and a lower buffer layer is provided between the substrate and thecore.

[0009] This can also be an improved semiconductor laser diode comprisinga semiconductor substrate; a core layer comprising an active region anda waveguide region on the substrate, the waveguide region beinglongitudinally-displaced from an active region, and wherein the activeregion comprises at least one quantum well; an upper cladding layer onthe core layer; a diffraction grating comprising grating fingersextending down into the top cladding layer over at least a portion ofthe waveguide region; and an integrated lens-grating wherein thelens-grating is spaced by at least one-hundred wavelengths from the topgrating from the diffraction grating.

[0010] This can also be a method of fabricating an improvedlight-generating semiconductor structure, the structure having top andbottom surfaces, the method comprising providing a semiconductorsubstrate; providing a core layer containing active-region, and awaveguide region longitudinally-displaced from an active region, thecore layer being over the substrate; providing an top cladding layer onthe core layer; providing a diffraction grating on the top claddinglayer over at least a portion of the waveguide region; and providing anintegrated lens-grating integrated into the diffraction grating or onthe bottom surface or in a coupling block. Preferably, the lens-gratingis spaced by at least one-hundred wavelengths from the diffractiongrating. In some embodiments, an output fiber is provided and thelens-grating directs an output beam into the fiber and the fiber may bea single-mode fiber.

[0011] In some embodiments, a grating-containing coupling block cut froma glass wafer is attached to the fiber, the chip, or both, and thecoupling block contains at least one grating selected from the groupconsisting of: a resonance-grating to reflect light back to the activeregion, a fiber-diffraction-grating to diffract light into the fiberalong the fiber axis, a diffraction-grating to diffract light into thecoupler and then into the fiber, a lens-grating, and a beam-shapinggrating.

[0012] In some embodiments, a coupling-block having opposing faces isprovided and one coupling-block opposing faces is attached to the fiberand the other opposing face is attached to the semiconductor structure.An integrated lens-grating may be within the coupling-block. The fibermay be attached to the coupling-block by a thermosettingoptically-transparent adhesive which was applied to the coupling-blockand/or the fiber and dried without being cured, and wherein the fiber isthen placed in contact with coupling block, and the thermosettingadhesive is then cured to bond the fiber to the coupling block.

[0013] The semiconductor structure may be attached to the coupling-blockby a thermosetting optically-transparent adhesive which was applied tothe coupling-block and/or the semiconductor structure and dried withoutbeing cured, and wherein the semiconductor structure is then placed incontact with coupling block, and the thermosetting adhesive is thencured to bond the semiconductor structure to the coupling block. Thethermosetting adhesive may be cured to bond the semiconductor structureto the coupling block at a position of essentially a maximum value oflight intensity in the fiber by UV curing.

[0014] In some embodiments, the diffraction grating diffracts light bothupwards and downwards and an integrated reflector directs both upwardsand downwards refracted light through the integrated lens-grating intothe fiber. In some other embodiments, the diffraction grating diffractslight both upwards and downwards and a topside integrated reflectordirects upwards refracted light through the integrated lens-grating intothe fiber.

[0015] A coupling block is preferably used herein to couple light fromthe chip to an output fiber, and preferably to couple feedback reflectedfrom the fiber back to the chip. For example, a one-part coupling blockcan be used between the chip (e.g., adjacent a glass-filled lowergrating) and a fiber, with the coupling block attached to both the chipand the fiber, with no grating on the coupling block. Alternately, aone-part coupling block can be used between a chip which does not have alower grating, and a fiber, with the coupling block attached to both thechip and the fiber, with an integrated lens-grating on the couplingblock surface that is attached to the bottom of the chip.

[0016] Another alternative is a one-part coupling block can be usedbetween a chip which does not have a lower grating, and a fiber, withthe coupling block attached to both the top chip surface and spaced fromthe fiber, with an integrated lens-grating on the coupling block topsurface. Thus one can have a one-part coupling-block may have, or maynot have, a grating on one of its surfaces. Still another alternative isto have a two-part glass coupling-block, with an internal gratingbetween the two parts between a chip which does not have a lowergrating, and a fiber, with the coupling block attached to both the topchip surface and the fiber.

[0017] One can also have coupling-blocks with more than on internal orsurface gratings and the coupling-blocks can have three or more parts.Both the top grating and the internal grating can aid in the shaping(e.g., Gaussian-distribution) of the beam (preferably all rays exitingthe top grating are parallel and any focusing is provided by a gratingspaced, e.g., by at least one-hundred wavelengths from the top grating).The use of an internal-grating coupling-block can provide such a spacedgrating. The use of a coupling block can eliminate all solid-to-airinterfaces in coupling light between the chip and a fiber, and caneliminate “facet-type damage” that can occur with high interface powerdensities.

[0018] Preferably, bonding of parts is done with optical glue (e.g.,optical epoxy) that is dried (the solvent generally is removed atmoderate temperature, preferably in a vacuum), but not cured (notcross-linked) on at least one of the surfaces to be bonded, prior toassembly of the parts. The parts are then assembled and held aligned (insome cases, the diode is energized and power in the fiber is monitoredduring alignment) and the glue cured, possibly thermally, but preferablyUV cured. While curing can be done in a vacuum, this is generally notnecessary if surfaces are properly prepared. Such bonding is preferablydone between fiber and coupling-block, and between coupling-block andchip, and is especially important in bonding involving and air-filledgrating (e.g., an internal grating between parts of a two-part grating)as using a glue that flows during assembly will generally flow glue intograting grooves and degrade or destroy the grating.

[0019] Wafer-scale production of gratings on a wafer (e.g., a glasswafer) may also be used to produce couplers. Amultiple-grating-containing wafer can be cut into small pieces(coupling-blocks). More than one such piece can be used in a coupler. Acoupler is preferably attached to fiber or a chip, and preferably both.The couplers can contain one or more gratings, and the gratings on acoupler can include; a resonance-grating to reflect light back to theactive region, a diffraction-grating to diffract light into the fiberalong the fiber axis, a diffraction-grating to diffract light into thecoupler and then into the fiber, a lens-grating, and a beam-shapinggrating. Such couplers can provide spacing along the light path andeliminate grating-to-grating interference, facilitating, for example,chip-top emission into a single mode fiber. Preferably no discreteoptical elements are used and all gratings are wafer-produced on thechip or on the fiber (or on a wafer-produced coupler attached to thechip or fiber), and as a result, costs are greatly reduced.

[0020] The foregoing has outlined rather broadly the features andtechnical advantages of the present invention in order that the detaileddescription that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter which formthe subject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and specific embodimentdisclosed may be readily utilized as a basis for modifying or designingother structures or processes for carrying out the same purposes of thepresent invention. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a more complete understanding of the present invention, andthe advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying drawing, inwhich:

[0022]FIG. 1 shows a view of a chip-diode laser with an externalfeedback mirror, which laser can be tuned by tilting the mirror;

[0023]FIG. 2 shows measured output intensity as a function of wavelengthin nm from a chip-diode laser;

[0024]FIG. 3 shows a measured output intensity as a function of angle atwhich the beam diverges, both longitudinally (parallel to the topcontact) and transversely (perpendicular to the top contact);

[0025]FIG. 4 shows a simplified longitudinal elevation cross-section ofa structure with a tapered electrode that can be used with or withoutexternal components;

[0026]FIG. 5 shows a top view of a device with a shaped top terminal(metal contact and electrode) and a shaped grating that can provide bothreflection control and beam shaping;

[0027]FIG. 6 shows a simplified elevation cross-section of a diodeshowing a grating shaping by varying the depth of grating fingers;

[0028]FIG. 7 shows an elevation cross-section with a top reflector andbottom-surface emission, and an ion-implanted grating;

[0029]FIG. 8 shows an elevation cross-section with a buried dielectricreflector and top-surface emission, and with the emission self-alignedinto an optical fiber;

[0030]FIG. 9 shows an elevation cross-section with a top reflector andbottom-surface emission, with a lower beam-shaping grating, and with theemission self-aligned into an optical fiber;

[0031]FIG. 10 shows an inverted simplified elevation cross-section of adiode, but using the same designations for like parts, with acoupling-block adjacent a “lower” grating that focuses light through acoupling block into a fiber, which fiber contains an embedded feedbackreflector;

[0032]FIG. 11 shows a simplified elevation cross-section of a diode withan upper diffraction grating focusing light through a coupling blockinto a fiber; and

[0033]FIG. 12 shows a simplified elevation cross-section of a diode withan upper grating diffracting light through a coupling block containing alens-grating that focuses the beam a into a fiber, which fiber containsan embedded feedback reflector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

[0035] This diode-chip-laser can provide narrow-band coherent light,(light that is virtually all in-phase and at, or essentially at, thesame wavelength). These grating-coupled diode improvement enable, forthe first time, combining of all the functional advantages ofnon-semiconductor-chip (e.g., fluid) lasers with the efficiency,economy, convenience, and the efficiencies ofsemiconductor-chip-manufacturing (wafer processing). These chipsgenerate light parallel to the top surface and utilize gratings thatdiffract light out top and/or bottom surfaces. Thus they have both along light generation region and a large output area, and can providesignificantly higher power than prior art semiconductor-chip diodes.

[0036] Our methods and devices make enhanced beam quality achievable inhigh-power solid-state diodes. Our structures can substantiallyeliminate the more significant stray reflections in laser-diode chips,and surprisingly, this has allowed the signal (generally the feedback)to be greatly reduced (as opposed to prior art designs that haveincreased the feedback to get coherent light), while allowingsignificantly greater output power than prior art laser-diode chips. Oursignal is preferably reduced to less than 4% of the output light forboth internally fed-back and externally fed-back devices, as well asoptical amplifier devices. The advantages of our designs generallyinclude: more efficient coupling of light from the core into the outputbeam; more coherent output beam; narrower line-width output beam; andgreater output power.

[0037] In external feedback embodiments, all internal reflections backinto the active region are preferably essentially eliminated (includinggratings with very-low reflectivity, preferably of less than 0.1% andmore preferably less than 0.01% of the output light).

[0038] Further, unlike prior art gratings designed to reflect light tothe active region, our gratings can be detuned to reduce not onlycertain stray, but also wanted (feedback) reflections from the gratings.In one type of embodiment, internal feedback is provided by the outputgrating, but the feedback is reduced to less than 4% of the outputpower.

[0039] These techniques can use a combination of an out-coupling(diffracting) grating and feedback from the output optical fiber toproduce directed lasing in which the output angle of light from the chipgrating aligns itself to the fiber input. The self-directed lasingespecially provides a chip-fiber longitudinal alignment that greatlyreduces costs, particularly when the fiber is a single-mode fiber with acore diameter of ten microns or less. A lens-grating (at least part ofwhich can be combined with the out-coupling grating) can be used toallow higher output power. Beam-shaping by one or a combination ofgratings can be used (some beam shaping can be done by a shaped topmetal contact as well), e.g., to provide a Gaussian distribution formore efficient coupling into a single-mode fiber. Controlling of chiptemperature can be used to control the output wavelength of the device.As noted, in some embodiments, the light distribution is also adjustedby non-linear patterning of the top contact and/or the grating entrance.One or more gratings integrated into the chip can be used to transfer abeam, preferably self-directed, from the chip directly into an opticalfiber, eliminating expensive, non-integrated optics.

[0040] A view of a chip-laser diode 20 with external feedback is shownin FIG. 1. The external feedback reflector 22 shown is a partiallyreflecting mirror, however some preferred embodiments use other types offeedback reflectors. Output light is shown by dashed lines and has agenerally cylindrical shape. The diode 22 has a top metal contact 24 ona top electrode 26.

[0041] Top cladding layer 28 has a diffracting grating 30 (thediffraction grating can be a series of grooves etched in the top surface32 of the top cladding layer 28). An active-region-containing core 34 isunder the top cladding layer 28. The active-region-containing core 34 isover (possibly with intervening layers, not shown) a semiconductorsubstrate 36.

[0042] Generally layers are epitaxially grown on a semiconductor waferfor the active-region-containing core 34, the top cladding layer 28, andthe top electrode 26; metal is deposited and patterned and etched forthe top metal contact 24 and bottom metal contact; a patterned etchexposes top surface 32 of the top cladding layer 28 leaving ananti-reflection-shaped top electrode output end 40; and the diffractinggrating 30 is patterned and etched as a series of grooves in the topcladding surface 32. The wafer is then cleaved into individual diodechips.

[0043] The active region is generally the portion of the core 34 that isunder the top metal contact 24. The waveguide region is generally asection of the core 34 that is under the diffracting grating 30 plus aconnecting part of the core 34 between the active region and the sectionunder the diffracting grating.

[0044]FIG. 2 shows light output as a function of wavelength, measuredfrom one such diode. FIG. 3 shows light output as a function ofwavelength, measured from one such diode.

[0045]FIG. 4 shows a simplified cross-sectional elevation about thelongitudinal centerline of a diode chip (generally herein, like partsare designated by like numbers). Note that the drawings are generallynot to scale. In this view, the bottom metal contact 38 can be seen onthe bottom of the substrate 36. The diffracting grating 30 (showngreatly enlarged and with only a small fraction of the number ofgrooves) has a period 42 and an output beam at an angle 44 fromvertical. The wavelength of the output light from a given quantum wellstructure is primarily a function of diffracting grating period 42,output beam angle 44, and chip temperature. The active region 46 isgenerally the portion of the core 34 under the top metal contact 24 andthe waveguide region 48 of the core 34 is also indicated. The chip hasan active-end facet 50 and a passive-end facet 52, which were formedduring the cleaving operation. The active-end facet 50 can serve as oneend of the laser-diode cavity, but the passive-end facet 52 in ourembodiments is generally isolated such that there is substantially noreflection from the passive-end facet 52 back to the active region 46.In some embodiments, the passive core-portion 54 (adjacent thepassive-end facet 52) is processed to be anti-reflective. Here theactive-end facet 50 is a reflector that serves as one end of the lasercavity and a mirror 22 that serves as the other.

[0046] In embodiments in which a device is to be an optical amplifierthere are no cavity end reflectors, and a device is fabricated which isessentially two back-to-back devices of FIG. 4, (mirrored about the lineof facet 50, but with no facet dividing the joined active regions, suchthat one grating can be used as an input, and the other as the output).Generally all the innovations herein incorporated can be used infabricating and/or packaging optical amplifiers or even Superlumedevices (which are broadband emitting devices which can use a FIG. 4structure, but do not use a narrowband feedback).

[0047]FIG. 5 shows a top view of a diode chip with a non-linearpatterned top terminal 56 (non-linear patterned top terminal 56 can beformed by patterning and then etching both the metal contact layer andthe top electrode layer) and a non-linear-patterned-entrance grating 58.Non-linear patterning can perform the functions of reflection-reductionand/or beam-shaping for either of, or both of, the top terminal 56 andthe non-linear-entrance grating 58. The light intensity distribution inthe output beam can be shaped, e.g., to give the beam a Gaussiandistribution for more effective coupling into, e.g., a single-modefiber. For example, making the top terminal “convex-shaped” on the end56 towards the grating, and the grating “convex shaped” on the end 58towards the top electrode can make both the electrode and the gratingends essentially non-reflective and help shape the beam distribution. Afiner sine-wave or other regular or irregular pattern can besuperimposed on, or even to replace the smooth curve shown. Withnon-linear patterning, the top metal contact and the top electrode canboth be dry etched (thus eliminating the less desirable wet processing)with a single patterning step. An A/R coating on the top electrode endcan also be used to reduce reflections into the active region, Theversion of the non-linear-entrance grating 58 uses grooves 41 a, 41 b,41 c, that shorter (fingers that are not as long) at the end nearer theactive region than the grooves 41 in the remainder of the grating(alternate versions use shallower grooves on this end).

[0048] Diffracting gratings can cause output light to be split intoupward diffracted light beams and downward diffracted light beams, andefficiency can often be increased by combining these beams with sometype of mirror (care needs be taken the obtain a generally in-phasecombination).

[0049]FIG. 6 shows a view similar to FIG. 4, but with a buriedmulti-layer dielectric mirror 60. The dielectric mirror 60 can havealternating layers (not shown) of materials with different dielectricconstants, epitaxially grown during wafer epitaxy. The dielectric mirror60 has a semiconductor spacer 62 (e.g., of the same material as thesubstrate) the dielectric mirror 60 is spaced to give in-phasecombination of the beams (at the angle of beam travel by aboutone-quarter of the “in-material” wavelength below the grating 30 orthree-quarters, one and one-quarter, etc., spacing). Note that FIG. 6shows grooves 41D, 41E, 41F, that shallower (fingers with less depth) atthe end nearer the active region than the grooves 41 in the remainder ofthe grating. Note also FIG. 6 shows the top metal contact 24 and the topelectrode 26 with cross-sections produced by dry etch in forming topterminal 56 and also shows shaped output-end of top metal contact 39 andanti-reflection-shaped top-electrode output-end 40 shaped by dryetching. The top metal contact 39 is shaped primarily for beam shaping.When the contact 39 and electrode are etched with a single patterning,the top-electrode output-end 40 may need additional anti-reflectiontreatment, such as doing the patterning with a finer sine-wave or otherregular or irregular pattern superimposed, and/or with an A/R coating,as noted above.

[0050]FIG. 7 also shows a view similar to FIG. 4, but with a top mirror64. The top mirror 64 is formed after the grating 30 is etch and has atransparent (at operating wavelength) material 66, such as silicondioxide, deposited in the grating grooves and over the top claddingsurface and a metallization 68 deposited on the transparent material 64.The top mirror 64 is spaced to give in-phase combination of the beams(e.g., by about one-quarter of the in “transparent material” wavelength,a 990 nm in air wavelength would be 660 nm in glass with an index ofrefraction of 1.5, or 165 nm/cosine Theta) below the grating 30. With atop mirror, the output beam passes down through the substrate and outthe bottom surface 70. As the transparent material 66 may have an indexof refraction less that one-half that of the semiconductor, thetransparent material 66 may be more than twice as thick as the spacer62. FIG. 7 also shows fingers 41 g that are ion-implanted regions. Ionimplantation done with helium or argon can convert crystallinesemiconductor material into amorphous material to provide gratingfingers with bottom portions extending down into the cladding over thepassive region of the core. Implantation can be patterned usingphotoresist.

[0051] The diffracting grating 30 can be modified be a combinationgrating that and does beam shaping as well as diffracts. FIG. 8 shows aview similar to FIG. 6, but with a combination grating 72 that diffractsand also focuses self-directed light into an optical fiber 74. Theoutput light is self-directed due to a novel arrangement that usereflected light from the fiber as feedback. The combination grating 72could also be used in an arrangement similar to FIG. 7, with focusedlight going out the bottom surface.

[0052]FIG. 9 shows a view similar to FIG. 7 (FIG. 9 also usesion-implanted fingers), with a spaced-set of upper and lower gratings76, 78, where the use of a spaced-set allows more flexible beam shaping,e.g., diffraction (generally in the upper grating 76) and alsoGaussian-distribution-adjusting and focusing in the combination of upperand lower gratings 76, 78. In some cases (not shown), a one-partcoupling block (which may or may not have a surface grating) can be usedbetween the chip (e.g., adjacent a glass-filled lower grating) and afiber. The lower grating 78 is shown in the substrate bottom andunfilled. The grating could also be in a silicon nitride or silicondioxide layer on the substrate bottom. In single mode operation, thelight rays are generally parallel to one another, when passing betweenthe upper grating 76 and the lower grating 78. The rays can beperpendicular to the bottom surface, or on angle (e.g., 17 or 25 degreesfrom vertical).

[0053] The configuration of FIG. 9 is preferred especially for low poweroperation, where high power-densities at air interfaces are not a majorproblem. Preferably the fiber is spaced at least 5, and more preferablyabout 6, mm from the chip. With higher power diode chips, a glasscoupling-block (not shown here) can be inserted between (and opticallyglued to) the chip and the fiber. With a coupling-block, the fiber endand/or top of block can be angled. The coupling-block can be a glassstub, preferably at least 3 mm long (e.g., of multi-mode fiber about 100micron diameter, preferably not graded-index, about 4 mm long). When acoupling block is used, there is preferably a controlled reflectivityjoint between the coupling-block and the fiber. Coupling blocks attachedby optical glue generally eliminate problems from high power-densitiesat air interfaces.

[0054] Alternately (also not shown), one can have top grating thatdiffracts and an internal (e.g., focusing) grating within a two-part,glass coupling-block. Both the top grating and the internal grating canaid in the shaping (e.g., Gaussian-distribution) of the beam (preferablyall rays exiting the top grating are parallel and any focusing isprovided by a grating spaced, e.g., by one-hundred wavelengths or morefrom the top grating). As used herein “spacing” in wavelengths is tomean wavelengths in the medium in which light is traveling, and thus thenominal output wavelength of the device corrected by dividing by theeffective index of refraction of the medium. The use of a coupling blockcan eliminate all solid-to-air interfaces in coupling light between thechip and a fiber.

[0055]FIG. 10 shows an inverted simplified elevation cross-section of adiode, but using the same designations for like parts. Thecoupling-block 82 is adjacent a “lower” grating 78. The grating 78focuses light onto the entrance of block-to-fiber stub 86. A feedbackreflector 92 is embedded between the block-to-fiber stub 86 and fiber74. The feedback reflector 92 is preferably at least 4 mm of opticalpath length from the “lower” grating 78, as our experiments have shownthis gives better results. The coupling block 82 has an A/R coating 90,and is attached to the lower-grating fill-glass 94 of the diode byblock-to-chip glue 84. The metallization 68 provides a mirror toincrease efficiency. Optical glue 88 attaches fiber 74 to coupling block82. This general arrangement can also be used for single-mode operationwithout the coupling block 82 (e.g., the coupling block 82, A/R coating90, lower-grating fill-glass 94, block-to-chip glue 84, and optical glue88 can be eliminated), but using the coupling block is preferred.

[0056]FIG. 11 shows a simplified elevation cross-section of a diode withan upper diffraction grating 76 focusing light through a coupling blockinto a fiber. Such an arrangement can be used for broadband emission,but tends not to give single-mode operation.

[0057]FIG. 12 shows a simplified elevation cross-section of a diode withan upper grating 76 diffracting light through a coupling block 82containing a lens-grating 98 and a coupling-block cap layer 96. Thelens-grating 98 focuses the beam into a stub 86 and fiber 74combination, which combination contains an embedded feedback reflector92. The buried multi-layer dielectric mirror 60 provides a mirror toincrease efficiency. Optical glue 88 attaches coupling-block cap layer96 to the stub 86 and the coupling-block 82. Like the arrangement ofFIG. 10, this arrangement can be used for single-mode operation.

[0058] We can use a flat grating-lens, and novel coupling-block-fiberunit to replace the difficult to align multiple separate (and expensive)components that have heretofore been used to couple light out of a laserdiode. Our arrangement needs only one accurate positioning and thatpositioning needs only two-dimensional alignment. The use of theinput-end of the fiber as the feedback reflector controls the lasingsuch that the output beam is directed into the fiber, and the spacingbetween faces assures that the beam is in focus when it reaches thefiber input-end. The flat surface of the lens allows the sliding ofcoupling-block-fiber over the surface and maintaining contact andcontinually measuring the light intensity while changing relativeposition between the lens and the coupling-block-fiber unit. When theposition of maximum output power is determined, and that position ismaintained while a rapid bonding process is used to bond thecoupling-block (and its attached fiber) to the lens (preferably, aglass-filled lens is used). The use of a flat lens and/or thecoupling-block with fiber unit provides an inexpensive and verypractical way of aligning the fiber while using a lens-grating with aneasily manufacturable far-field focal length.

[0059] These techniques preferably use a combination of an out-couplingdiffracting grating and feedback from the output optical fiber toproduce directed lasing in which the output angle of light from the chipgrating aligns itself (or allows thermal aligning) to the fiber input.The self-directing fiber-feedback eliminates the need for criticallyaligning of each of multiple components in three-dimensions in packaginga diode (previously, this positioning has required tedious manualassembly). In some embodiments, coupling angle is self-directed and finetuning of wavelength can be done by chip temperature. In some otherembodiments, the wavelength is determined by the fiber and couplingangle is fine tuned by chip temperature. In either case, assembly isgreatly simplified, and parts are eliminated (temperature controllersare not an extra part added, as they are essentially always used withsuch diodes). The directed lasing especially provides a chip-fiberangular alignment that greatly reduces costs, particularly when thefiber is a single-mode fiber with a core diameter of ten microns orless. In addition, some embodiments use a novel side-input on the outputfiber that allows a long fiber-input, including lengths that are longerthan the output beam, making the longitudinal alignment relatively easyas well, which further reduces costs.

[0060] A lens-grating (which can be combined with the out-couplinggrating, especially in non-single-mode applications) can be used toallow higher output power. Beam-shaping grating can be used as well,e.g., to provide a Gaussian distribution for more efficient couplinginto a single-mode fiber, and can be accomplished using a combination ofgratings, generally including grating that provide other functions aswell.

[0061] Directed lasing can be established which directs a coherentlasing light beam into the fiber. In some embodiments, the fiber-inputface is substantially parallel to the axis. In many embodiments, afiber-diffraction-grating on the fiber-input face or a chip bottom-sideoutput-surface refracts light into the fiber along the axis. In someembodiments, generally including embodiments where the fiber is attachedto a chip output-surface with optical glue, the grating is designed todiffract light at an angle (e.g., 25 degrees) that the difference inindexes of refraction between the semiconductor chip (e.g., GaAs) andthe glass of the optical fiber refracts the light down the axis of thefiber. A positioner may be used to provide a relative angle between thefiber-input-face and the horizontal out-coupling grating, and standardsemiconductor chips are manufactured and different nominal wavelength oflight devices are produced by selecting different relative anglepositioners. A chip-temperature controller may be used in conjunctionwith the relative angle to determine the wavelength of light from thesemiconductor chip.

[0062] In some alternate embodiments, the wavelength of light from thesemiconductor chip is determined by a resonance-grating on or in thefiber, which resonance-grating produces a resonance-determiningwavelength of light that is fed back to the active layer. Wafer-scaleproduction techniques (using semiconductor wafer production equipment)are preferably used in all gratings, including any grating on thefibers. Gratings can be defined by lithography and etched, on shortlengths of fiber assembled into wafer form (the short lengths of fibercan, of course, easily be joined later to longer lengths). Wafer-scaleproduction of gratings on a wafer (e.g., a glass wafer) may also be usedto produce grating-containing light couplers that can be cut into smallpieces. More than one such piece can be used in a coupler. A coupler ispreferably attached to fiber, a chip, or both. The couplers can containone or more gratings, and the gratings on a coupler can include; aresonance-grating to reflect light back to the active region, adiffraction-grating to diffract light into the fiber along the fiberaxis, a diffraction-grating to diffract light into the coupler and theninto the fiber, a lens-grating, and a beam-shaping grating. Suchcouplers can provide spacing along the light path and eliminategrating-to-grating interference, facilitating, for example, chip-topemission into a single mode fiber. Preferably no discrete opticalelements are used and all gratings are wafer-produced on the chip or onthe fiber (or on a wafer-produced coupler attached to the chip orfiber), and as a result, costs are greatly reduced.

[0063] This can be a method of coupling light out of a laser-diode chipinto an optical fiber, the method comprising preparing a diode chip witha top side and a bottom side and output grating on the top side;integrating a digital lens with a flat lower surface and having a focallength into the bottom side of the laser-diode chip; preparing a glasscoupling-block with first and second opposing coupler-faces spaced apartby the digital-lens focal-length; attaching a glass fiber to the firstcoupler-face; placing the second coupler-face in contact with thedigital lens in the fiber, and maintaining the contact and continuallymeasuring the light intensity while sliding the coupler on the digitallens in two dimensions; and determining a position of maximum lightintensity in the fiber and bonding the digital lens to thecoupling-block essentially at the position of a maximum of lightintensity.

[0064] This can also be a method of coupling light out of a laser-diodechip into an optical fiber, the method comprising preparing a diode chipwith a top side and a bottom side and output grating on the top side;integrating a digital lens having a focal length on a top side or thebottom side of the laser-diode chip or both; preparing at least onecoupling-block with first and second opposing coupler-faces spaced apartby the digital-lens-focal-length; attaching an optical fiber to thefirst coupler-face; placing the second coupler-face essentially incontact with one of the digital lens in the fiber and maintaining thecontact and continually measuring the light intensity while changingrelative position between the digital lens and the coupler; and bondingthe digital lens to the coupler at a position of essentially a maximumvalue of light intensity in the fiber.

[0065] The fiber can be a single mode fiber. The fiber can be attachedto the coupling-block by an optically-transparent adhesive. Thecoupling-block can be attached by an optically-transparent adhesive. Thetop grating can diffract light both upwards and downwards and anintegrated reflector can be used to direct both upwards and downwardsrefracted light through the integrated lens into the fiber. Thelens-grating (preferably glass filled) can be attached to thecoupling-block by a thermosetting optically-transparent adhesive whichwas applied to the coupling-block and/or the lens and dried withoutbeing cured, and wherein the thermosetting adhesive is then cured tobond the lens to the coupler at a position of essentially a maximumvalue of light intensity in the fiber, preferably by UV curing.

[0066] In one type of embodiment, a single-mode fiber has an input thathas been through a lens-grating and a beam-shaping grating, and both arespaced from the fiber, (the single-mode fiber is not be direct-connectedto the chip), and the emission is out the bottom of the chip. If thefiber input-face is on a side of the fiber, the fiber may have an inputdiffraction-grating. The resonance-producing reflection may be from thefiber input-face, or a resonance grating in the fiber. The fiber may beused with input-face non-normal to the beam or with a face having an A/Rcoating.

[0067] The above type of embodiments can also generally be used with amulti-mode fiber. With a multi-mode fiber, some preferred embodimentsare used without a beam-shaping grating, and a combinationlens-and-diffraction grating can be used and the emission could be outthe top surface or bottom, including a fiber directly attached to thebottom of the chip. If direct chip attachment is used, there could be aninput diffraction grating on the fiber or on the chip bottom, or thelight angle could be such that refraction (e.g., a 25 degree refraction)between the chip and the fiber sends light down the fiber. If directchip attachment is used, a resonance grating in the fiber can be used toprovide the feedback reflection for self-direction of the output beaminto the fiber.

[0068] In one experiment, a fiber-end-face was used to reflect aresonance-inducing portion of the light back through the grating to theactive layer. A two-part positioner was used to provide a relative anglebetween the fiber-input-face and the horizontal out-coupling grating.The two-part positioner served to dissipate heat from both thesemiconductor chip topside and bottom side. A thermoelectricchip-temperature controller was used in conjunction with the relativeangle to determine the wavelength of light from the semiconductor chip.In this experiment, light was self-directed and produced efficientcoupling and single-mode emission.

[0069] For single mode emission, we generally have used two separategratings, one to beam-shape to Gaussian, and one to match spot size tofiber surface, into either single-mode or multi-mode fiber (note,however, one can reasonably efficiently couple non-Gaussian beam into amulti-mode fiber and thus one can use a fiber end-face reflection andonly one, diffracting and focusing, grating). In any case, preferablytwo separated gratings are used to couple into a single-mode fiber.

[0070] A focusing (and diffracting) top-grating can be used with aGaussian-shaping grating on the chip-bottom. Some embodiments use agrating on the fiber-surface (which also diffracts) on side of fiber. Atoptical powers higher than some level, typically a few watts, with anair-solid interface one will need a grating on the side of the fiber ispreferred to increase the area of the fiber input surface. Aresonance-grating in the fiber minimizes wavelength changes withtemperature, can provide some self-direction to beam into attachedfiber, and is convenient for giving a low level (e.g., 1%) feedbacksignal.

[0071] Use of fiber-side-surface can increase transfer area byprojection of elliptical spot and thus avoid “facet-damage”, butpreferably has a fiber-input diffraction-grating unless attached withoptical glue and at 25 degrees. A resonance-grating in fiber, especiallyif attached with optical glue, can give self-directed light. Atemperature control to maintain proper angle is preferred, as otherwise,coupling efficiency may be reduced. The 3^(rd) order diffraction of theout-coupling grating is eliminated by a beam of about 17 degrees (fromnormal). The bottom grating can beam shaping (e.g., Gaussian-adjusting)and the top grating both focusing and diffracting (the beam shaping canalso be in the top grating and the focusing in the bottom grating). Asused herein, the term “lens-grating” means a substantially-flat lenses(including Fresnel lenses, digital lenses, and an array of micro-lensfabricated by photoresist reflow and transfer etch, as well as gratings,including implanted, that perform a lens function of changing the areaof a beam of light as a primary function, and the term “beam shapinggrating” means a grating which has changing the distribution of light ina direction transverse to the direction of propagation (e.g., from askewed distribution to a Gaussian distribution) as a primary function.As such lenses can be used together to give a desired result, two (ormore) lenses can both contribute to both functions, and either lens canbe described by either term.

[0072] Reflection from a fiber-input (a face normal to light) can beused as feedback, rather than resonance-grating in fiber, withtemperature adjusted to control wavelength. This allows increasedtransfer area, and can use a fiber diffraction-grating, without afiber-resonance grating.

[0073] This is a relatively simple arrangement that avoids“facet-type-damage” in the low, e.g., 1 to 20 watt, power output range.Alternately, the use of a resonance-grating in a fiber-side-surface canprovide self-directed light. The fiber may be attached to the chip, orin air. The fiber-input can be a tapered fiber section which tapersfrom, e.g., a 100 micron diameter input face to, e.g., a nine microndiameter which can be butt-attached to a standard single-mode fiber.Self-direction of light allows for loose tolerances. In x and y, thetransfer spot can slide along output area, and alignment is relativelyeasy. Optical gluing of a coupling-block needs no z-alignment, and asthere is no solid/air interface, thus “facet-damage”, is generally not aproblem, and this can give very high power capacity. Note that alignmentfor effective coupling directly into a single-mode fiber face (e.g., 9micron core diameter) generally requires a 1 micron accuracy. For suchdevices, a 10 micron tolerance can be “relatively easy”.

[0074] One bottom-emission example uses a combination diffraction andfocusing grating on the top side and a multi-mode fiber attached to thebottom side. With resonance-grating in fiber, light is self-directed.This can have self-directed light when coupling angle is close to 25degrees and no lower refraction-grating is used. Preferably atemperature control is used to maintain diffraction angle of top-gratingto maintain good coupling.

[0075] Another bottom-emission example uses defraction/1-D focusingtop-grating, a Gaussian-adjusting bottom grating, a single-mode fiberand fiber-side input-face in air on the bottom side. Withresonance-grating in fiber, light is self-directed. This uses adiffraction-grating on the fiber-input. Preferably a temperature controlis used to maintain a diffraction angle of top-grating that gives goodcoupling. The fiber input face in air, need not be parallel to chipoutput surface, as long as fiber input-grating is appropriate for beamentrance angle. The use of fiber input face at non-normal angle to thelight beam avoids surface reflection feedback to active region, (and canstretch transfer-spot ellipse), allowing more power without“facet-damage” than fiber-end approach, but care needs be taken thatlight not be excessively reflected in other directions and wasted (e.g.,an A/R coating can be used).

[0076] If the wavelength is controlled by resonance-grating, andtemperature controlled by a thermoelectric cooler, one can control bysensing temperature or by sensing and maximizing power in the fiber.

[0077] If all gratings are to be on the chip or on the fiber and thefiber is a multi-mode fiber, it may be used without a beam-shapinggrating. Thus a combination lens-and-diffraction grating could be usedand the emission could be out the top surface or bottom, and a bottomattached fiber could be used. If direct chip attachment is used, therecould be an input diffraction grating on the fiber or on the chipbottom, or the light angle could be such that refraction sends lightdown the fiber. If direct chip attachment is used, a resonance gratingin the fiber is needed to provide the feedback reflection forself-direction of the output beam into the fiber.

[0078] In preferred embodiments, the lower portion of the core isprovided by a lower graded index layer and the upper portion of the coreis provided by an upper graded index layer. In some top-emittingembodiments the buried dielectric mirror is epitaxially grown beneaththe core during wafer fabrication. The grating normally causes light togo, not only out the top surface, but also down into the substrate, butthe mirror directs all light out the top, increasing efficiency. Themirror is at a depth that light going down into the substrate isreflected out the top surface, and is generally in-phase with the otherlight going out the top surface. The depth of the mirror is preferably afunction of the angle (theta, from vertical) at which the light exitsthe surface (4 sine Theta times the wavelength). If the light exit angleand the wavelength are adjustable, the depth can be set for the centerof the adjustment range. A top mirror (and bottom emission) isconvenient to give a mirror closer to the top grating, and is better atlow angles from the horizontal than buried dielectric mirror (and topemission), as offset of reflected beam is less.

[0079] In some preferred embodiments, where the grating fingers areformed by changing portions of the crystalline semiconductor (with anindex of refraction typically above 3) into an amorphous state (with anindex of refraction typically about 1.5), the ion implantation is with,e.g., helium or argon. Preferably implantation angled at between 2 and10 degrees from vertical is used to produce slanted fingers tiltedbetween 2 and 10 degrees from vertical.

[0080] In GaAs substrate embodiments, prior art gratings have generallybeen in an AlGaAs layer. In most preferred GaAs embodiment, our diodeshave an InGaP layer epitaxially grown over (preferably directly on thetop of) the core (in particular over a GRIN layer which is the top ofthe core). This can provide an etch-stop-layer for accurate verticallocation of the top the grating, and, when a grating is etched into it,provides an aluminum-free grating (avoiding problems of aluminumoxidation), and also enables fabrication of saw-tooth gratings usinganisotropic etching of InGaP.

[0081] In external cavity embodiments, the reflection from the gratinginto the active region is reduced, preferably to less than 0.1 percentof the intensity of the light entering the waveguide from the activeregion (and more preferably to less than 0.01%, and still morepreferably to less than 0.001%). This can be done by at least one of thefollowing: a combination of grating spacing and finger depth to reducethe zero-order and second-order of the grating to at least near minimumfor the operating wavelengths; increasing the vertical distance betweenthe grating and the core; and using a grating with saw-tooth orsinusoidal cross-section. In many such embodiments, the reflector isplaced 5 or 6 mm from the diffraction grating and may placed within anoptical fiber.

[0082] By lowering reflections from the output grating, the passive-endfacet, the electrode end nearest the grating, and the grating-endnearest the active region, a very low intensity feedback signal can beused. Typically Fabre-Perot diodes use a feedback of about 30 percent ofthe intensity of the light exiting from the active region. Outputgratings of grating-coupled diodes are generally designed to “optimize”(increase) their reflectance, generally to 20 or 30%. Our technique usesless than 10% (and more preferably to less than 4%, and still morepreferably to less than 1%). Prior art lasers typically have about 90%intensity at the facet near the electrode and are limited in power byintensity-related facet damage. Our diodes preferably have between 10%and 20% of active-region-output intensity at the electrode end facet(and far less at the passive-end facet).

[0083] While the passive-end-reflectors of our cavities are preferablyfacets (especially metallized facets), these techniques can also be usedwith Bragg gratings as the active-end-reflector.

[0084] Our grating can couple output light “vertically” out of ahorizontal-active-region (e.g., quantum well) device. They minimize lossand noise producing reflections back into the active region. Strayreflections may be eliminated, e.g., by dispersing or absorbing thelight. This minimizing the loss and noise producing reflections, allowsthe desired feedback reflections to be reduced as well. Power output ina typical edge-emitting diode is generally limited by facet damage onthe active-end facet, while our surface output area is much larger andallows much higher output. Power output in prior surface-emitting lasershas been limited by facet damage on the passive-end facet. Our loweringof the feedback lowers the power at this facet, and allows higher outputpower. While some diodes use Bragg gratings as reflectors in place ofthe active-end facet, these are more difficult to fabricate and lessreflective than metallized facets, and thus such diodes are generallyboth more expensive and less effective than our devices.

[0085] Such a grating can also be constructed in a manner that allowsthe grating to interact with the electromagnetic radiation in the coreof the diode producing an imbedded optical element (e.g., etalon and/orechelette) in a solid-state diode. The design of this intra-cavityoptical element can allow the modification of the emission laser diodeto produce, e.g., very-narrow-line-width light, similar to any of themodifications which have been done in fluid lasers (including partiallygas, partially liquid, dye lasers), but never before integrated withinthe solid state device.

[0086] Generally, this is a horizontal cavity laser diode structure withtop and/or bottom surface output. Electrically-pumped, diode structurescan be made in a traditional manner on a wafer of the desiredsemiconductor material. A high spatial resolution grating can be exposedin photoresist onto the top surface of the structure, here, over thepassive region, but not over the active region, utilizing e.g., anangled 5 degrees from vertical RIE etching. While the grating can beleft unfilled, in some embodiments, grating is then filled, e.g., with aSiO₂ glass with an index of refraction ˜1.5, deposited, e.g., by CVD(e.g., PEMOCVD).

[0087] A mechanically tunable configuration of figure was successfullyused in experiments to prove the viability of the concept utilizing anexternal optical element. “Mechanically tunable”, as used hereingenerally means changing the output wavelength other than by changingthe temperature of (at least a portion of) the laser diode or bycontrolling a current passing through the laser diode. An essentiallynon-reflecting grating coupled light out (and back in from the mirror).Feedback and passive-end reflection was provided by a movable external,partially-reflecting mirror.

[0088] The core, e.g., in a single quantum well GaAs diode may be 0.4micron high (a little over one wavelength high for the wavelength inthis medium) and contain lower and upper GRIN layers below and above a 6nanometer quantum-well. There also may a lower semiconductor claddinglayer about 1 micron high of e.g., AlGaAs) below the core. The portionof the core directly below the upper electrode is the active region andthe remainder of the core is sometimes described as a passive region.The passive region is longitudinally-displaced from the active region.The upper semiconductor cladding may be an AlGaAs layer, but ispreferably InGaP, e.g., 0.3 micron thick. The top electrode 26, ispreferably of highly doped semiconductor. The grating in uppersemiconductor cladding has spaced fingers (there were actually hundredsof fingers in our experiments, but only about five are shown for drawingconvenience). When a voltage is applied between the top and bottomelectrodes, light is generated in the active region. The length gratingis preferably at least one-and-a-half times as long (e.g., 600 microns)as the active region (e.g., 300 microns). The grating fingers 36 mayhave tilted sides and bottoms to reduce the reflection from the gratingback into the active region. A 2 to 10 degree tilt has been found to aidin reducing stray reflection from the grating.

[0089] Preferably, the electrode material is highly-doped semiconductorand has a metal contact on the outer surface. In one preferredembodiment, the metal directly on the highly-doped semiconductor istungsten deposited by CVD (preferably using hydrogen reduction fromtungsten hexafluoride). The CVD deposition of tungsten is described inU.S. Pat. No. 3,798,060 “Methods for fabricating ceramic circuit boardswith conductive through holes” by Reed and Stoltz. The surface of thetungsten may then be coated with gold (also described in the abovepatent) or first nickel, then gold. Molybdenum-copper andtungsten-copper can also be used over the CVD tungsten. This tungstenmetal contact system may be used as part of the top contact, the bottomcontact, or both.

[0090] A grating design principle for a tunable configuration of FIG. 1was based on the grating equation: d(n_(eff)−Sine Theta)=kλ, where k isdiffracted order and is an integer, λ is the wavelength of theelectromagnetic radiation, d is the grating period (see 42 of FIG. 4,the start of one finger to the start of the next), n_(eff) is theeffective index of refraction of the grating (generally experimentallydetermined, but generally only slightly less than the semiconductormaterial of the cladding, e.g., here 3.29 as compared to the 3.32 ofGaAs) and Theta (output beam angle from vertical, 44 of FIG. 1) is theangle of the feedback mirror. The bottoms of the fingers utilized may beslanted at 5 degrees from the horizontal. The slant is preferably atleast 1 degree and is more preferably between 2 and 10 degrees (becauseof the angled etch, the walls were also slanted at about the sameangle).

[0091] Etching channels for the fingers in the top cladding can createthe grating. The fingers pass into the upper optical guiding cladding.The design of the grating takes into account the period, depth, aspectratio, terminating shape, and index of refraction of the semiconductormaterial and grating filling material. In the internal fed-back devices,the frequency of the diode can be influenced by the angle of thetermination plus other elements of the structure of the grating.

[0092] The structure controls reflection of optical noise (strayfrequencies) into the active region of the laser diode. Three differentsources of optical feedback (noise) due to reflections are: thereflection due to the termination of the top electrode, the reflectionfrom the facet at the passive end of the core, and unwanted reflectionsfrom the output grating.

[0093] Controlling the shape of the top electrode at the termination cancontrol the reflection due to the termination of the electrode (in theprior art it has been flat and perpendicular to the light in the core).The major at contribution to this effect is the end of the top electrodeclosest to the output region. The top electrode end closest to theoutput region may be shaped so that it is tapered with depth toward thepassive region (see FIG. 4) by a wet etch. Conceptually, this can belike the termination of a microwave structure in a horn to controlreflections. While the opposite end could be tapered in the oppositedirection, this has not yet proved necessary. A non-flat shaping (inplan view, see FIG. 5) can be used and can be dry etched. These shapingscan be alternately or in combination.

[0094] The second noise is the reflection of light from facet 52 at theend of the passive region of the structure. The combination of thegrating design and the length in the passive region can create a devicestructure such that allows very little light reaches the facet 52 at theend of waveguide/passive region of our device. This dramatically reducesthe optical noise that is reflected to the active region. This is incontrast to traditional edge emitting diodes or Bragg grating de-coupleddiodes that use this facet as one of the reflectors of the resonatorcavity of the laser.

[0095] In the past, the reflection from the grating has been a maximizedsignal to be larger than the other sources of reflection. In ourpreferred structures, the other reflections are substantially eliminatedand the grating reflection is reduced. This allows a low feedbackreflection for internal cavity devices and substantially eliminatedreflection for external cavity devices.

[0096] In one embodiment, a diode structure was designed to control thereflections to produce a diode with no external components and thefeedback reflection was provided by the grating. The grating in thisexample is to be reflecting and thus the grating constant d may equalkλ/n_(eff), such that the output light was essentially normal to thesurface. Even thought the grating is reflecting back into the activeregion, the reflection is reduced as described herein to less than about4% of the power from the active region.

[0097] Even with a diffracting grating 30, unless appropriate measuresare taken (e.g., greater grating 30 length, greater passive core-portion54 length, adsorbing of light via reverse biased electrode above andbelow the passive core-portion 54 or via ion-implantation of the passivecore-portion 54, wet etch taper of the passive core-portion 54, and/oranti-reflective coating of passive-end facet 52, there is somereflection from the passive-end facet, and a higher feedback from thegrating is required to avoid the above broadband emission. Our preferredcore and grating can be about 100 microns wide.

[0098] Material in the quantum well layer in the waveguide regionabsorbs light at the output wavelength, and while some is reemitted,some inefficiency results. Efficiency can be improved by disorderingthis material. This can be done by implanting ions down through the topsurface and into this area (while shielding the active region, e.g.,with photoresist). As such ion implantation generally lowers thetransparency of the waveguide, it is preferable to anneal the structureafter ion implantation. The preferred procedure is rapid thermal anneal(RTA) by one or more short pulses of high intensity light from tungstenlamps (again while shielding the active region). while this disorderssuch parts of the quantum well layer, it can generally done so as not torequire an anneal after the treatment (the high intensity light is broadband, but the waveguide, other than the quantum well layer, isrelatively transparent to the light and much more of the energy isabsorbed in the quantum well, as compared to the rest of the waveguide).Such parts of the quantum well layer can also be disordered by“laser-induced-disordering” by energy from a laser tuned to theabsorption wavelength of the quantum well, and, as the energy absorptionin the device being treated is principally in the quantum well layerbeing disordered, a post-anneal is generally not required.

[0099] Optical filters can be used with RTA to substantially eliminatelight of unwanted wavelengths (especially wavelengths which heat thenon-quantum well parts of the waveguide). The RTA is effective, cheaper,and faster, and is preferred.

[0100] In some, especially mechanically-tuned-diode, embodiments, thiscan be a method or laser diode that generates light within a III-Vsemiconductor structure at a wavelength of about 1550 nm and diffractslight out a top and/or bottom surface of the semiconductor structure,and includes: using an InP semiconductor substrate; a horizontal corelayer comprising an active region and a passive region, an uppercladding layer; and applying a voltage between top and bottom metalcontacts, whereby light is generated in the active region and asubstantial portion of the generated light is transferred out a topsurface over the passive region. Generally, all layers except thequantum-well-containing layer, and, are lattice matched. In someembodiments, an upper AlGaAS buffer layer is provided between the topcladding layer and the core and a lower AlGaAS buffer layer is providedbetween the substrate and the core.

[0101] Generally the semiconductor laser diodes are of III-V compounds(composed of one or more elements from the third column of the periodictable and one or more elements from the fifth column of the periodictable, e.g., GsAs, AlGaAs, InP, InGaAs, or InGaAsP). Other materials,such as II-VI compounds, e.g., ZnSe, can also be used. Typically lasersare made up of layers of different III-V compounds (generally, the corelayer has higher index of refraction than the cladding layers togenerally confine the light to a core). Semiconductor lasers have beendescribed, e.g., in Chapter 5, of a book entitled “Femtosecond LaserPulses” (C. Rulliere—editor), published 1998, Springer-Verlag BerlinHeidelberg New York. The terms “patterning” or “patterned” as usedherein generally mean using photoresist to determine a pattern as insemiconductor type processing.

[0102] Traditionally, edge-emitting laser-diode chips optically coupledthrough lenses to output fibers, have provided output light (“laseremission”) horizontally, with good energy efficiencies, reasonableyields, and the laser chip manufacturing efficiencies of waferprocessing. Most edge-emitting laser diodes have a semi-reflecting(about 30% reflecting) passive-end (far end) facet, which provides boththe output of the edge-emitting laser diode and the feedback Someedge-emitting lasers have used gratings as near-end (end nearer theactive region) reflectors for the cavity and/or stabilizing(wavelength-narrowing) feedback, but not for output coupling. Theirstabilizing feedback back to the active region is generally about 30% ofthe light from the active region from the exit facet to give anarrow-band emission. In some other cases the stabilizing feedback hasbeen from a fiber-optic pigtail, external to an edge-emitting chip,e.g., with an A/R (anti-reflecting) coating on the exit facet. Althoughdifficult to align with the output fibers (unlike grating-coupleddevices, edge-emitting diodes do not couple effectively through a rangeof angles), these device designs have worked well for multiplewavelengths with a variety of materials such as GsAs, InP, and others.

[0103] Generally, our wafer scale processing techniques producechip-laser-diodes with a diffraction grating that redirects output lightout the top and/or bottom surfaces. Noise reflections are carefullycontrolled, allowing significant reduction of the signal fed to theactive region. Generally, a diffraction grating and integratedlens-grating are used herein to couple light from the chip to an outputfiber, and the lens-grating is spaced from the diffraction grating.Preferably the diffraction grating and integrated lens grating are alsoused to couple light from the output fiber back to the active region ofthe chip.

[0104] The integrated lens-grating can be in a coupling block. The useof a coupling block can eliminate all solid-to-air interfaces incoupling light between the chip and a fiber, and can eliminate“facet-type damage” that can occur with high interface power densities.A coupling block is generally used herein to couple light from the chipto an output fiber, and preferably to couple feedback reflected from thefiber back to the chip.

[0105] In addition to very high power coherent light, ourgrating-coupled diode also enables additional gratings and/or lenses onthe top or bottom of the diode utilizing wafer scale processes. Thisdramatically reduces or even eliminates the need for the discreteoptical elements traditionally required to couple light into a fiber andthe need for critically aligning of each of multiple components inthree-dimensions in packaging a diode (previously, this positioning hasrequired tedious manual assembly).

[0106] Combination gratings and additional gratings and/or integratedlenses on the top or bottom of the diode can also be made utilizingwafer scale processes, reducing or even eliminating the need for theexpensive discrete optical elements traditionally required to couplelight out (e.g., into an optical fiber) and reducing alignment problems(prior art packaging of a diode has required tedious manual positioningof discrete optics). The diffraction grating can redirect a novelfeedback from the optical output (e.g., fiber) to produce lasing thataligns itself to the fiber input, and such self-aligned lasing furtherreduces assembly costs.

[0107] The examples used herein are to be viewed as illustrations ratherthan restrictions, and the invention is intended to be limited only bythe claims. For example, the invention can apply to other semiconductormaterials such as II-VI compounds. In some embodiments of a GRaded INdex(GRIN) structure is used. In some embodiments, an hiP laser diodegenerates light within a III-V semiconductor structure at a wavelengthof about 1550 nm out a surface of the semiconductor structure. Note alsothat the fingers of the grating can be silicon dioxide glass and thuscan have an index of refraction the same as that of the optical fiber,or can be filled with air.

[0108] Although the present invention and its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. An improved method of horizontally generatinglight within a semiconductor structure, and diffracting at least aportion of the generated light out of said structure and into an opticalfiber, said method comprising: providing a semiconductor substratehaving a substrate with a bottom surface and having a lower metalcontact on at least a portion of said substrate bottom surface;providing a core layer containing active-region, a waveguide regionlongitudinally-displaced from an active and a passive region with anadjacent passive-end facet, said core layer being over said substrate;providing an top cladding layer on said core layer; providing a topelectrode layer over said top cladding layer; providing a top metalcontact on a portion of said top electrode layer over said activeregion; providing grating fingers extending down into said top claddinglayer over at least a portion of said waveguide region to provide adiffraction grating; providing an integrated lens-grating wherein thelens-grating is spaced by at least one-hundred wavelengths from the topgrating from the diffraction grating; providing an optical fiber; andapplying a voltage between said top and bottom metal contacts, wherebylight is generated in said active region and at least a portion of thegenerated light is diffracted out of at least one of said cladding uppersurface and said substrate bottom surface, and focused into said fiberby said lens-grating.
 2. The method of claim 1, wherein saidlens-grating is on said substrate bottom.
 3. The method of claim 1,wherein a coupling block with said optical fiber attached, is connectedto said chip.
 4. The method of claim 3, wherein said lens-grating is insaid coupling-block.
 5. The method of claim 3, wherein said lens-gratingis on said substrate bottom.
 6. The method of claim 1, wherein saiddiffraction grating and integrated lens-grating are also used to couplelight from the output fiber back to the active region of the chip. 7.The method of claim 1, wherein an upper buffer layer is provided betweensaid top cladding layer and said core and a lower buffer layer isprovided between said substrate and said core.
 8. An improvedsemiconductor laser diode, said laser diode comprising: a semiconductorsubstrate; a core layer comprising an active region and a waveguideregion on said substrate, said waveguide region beinglongitudinally-displaced from an active region, and wherein said activeregion comprises at least one quantum well; an upper cladding layer onsaid core layer; a diffraction grating comprising grating fingersextending down into said top cladding layer over at least a portion ofsaid waveguide region; and an integrated lens-grating wherein thelens-grating is spaced by at least one-hundred wavelengths from the topgrating from the diffraction grating.
 9. A method of fabricating animproved light-generating semiconductor structure, said structure havingtop and bottom surfaces, said method comprising: providing asemiconductor substrate; providing a core layer containingactive-region, and a waveguide region longitudinally-displaced from anactive region, said core layer being over said substrate; providing antop cladding layer on said core layer; providing a diffraction gratingon said top cladding layer over at least a portion of said waveguideregion; and providing an integrated lens-grating integrated into saiddiffraction grating or on said bottom surface or in a coupling block.10. The method of claim 1, wherein a grating-containing coupling blockcut from a glass wafer is attached to said fiber, said chip, or both,and said coupling block contains at least one grating selected from thegroup consisting of: a resonance-grating to reflect light back to theactive region, a fiber-diffraction-grating to diffract light into thefiber along the fiber axis, a diffraction-grating to diffract light intothe coupler and then into the fiber, a lens-grating, and a beam-shapinggrating.
 11. The method of claim 9, wherein an output fiber is providedand said lens-grating directs an output beam into said fiber.
 12. Themethod of claim 11, wherein the fiber is a single-mode fiber.
 13. Themethod of claim 11, wherein a coupling-block having opposing faces isprovided and one coupling-block opposing faces is attached to the fiberand the other opposing face is attached to the semiconductor structure.14. The method of claim 13, wherein an integrated lens-grating is withinthe coupling-block.
 15. The method of claim 11, wherein the diffractiongrating diffracts light both upwards and downwards and an integratedreflector directs both upwards and downwards refracted light through theintegrated lens-grating into the fiber.
 16. The method of claim 11,wherein the diffraction grating diffracts light both upwards anddownwards and a topside integrated reflector directs upwards refractedlight through the integrated lens-grating into the fiber.
 17. The methodof claim 13, wherein the fiber is attached to the coupling-block by athermosetting optically-transparent adhesive which was applied to thecoupling-block and/or the fiber and dried without being cured, andwherein the fiber is then placed in contact with coupling block, and thethermosetting adhesive is then cured to bond the fiber to the couplingblock.
 18. The method of claim 13, wherein the semiconductor structureis attached to the coupling-block by a thermosettingoptically-transparent adhesive which was applied to the coupling-blockand/or the semiconductor structure and dried without being cued, andwherein the semiconductor structure is then placed in contact withcoupling block, and the thermosetting adhesive is then cured to bond thesemiconductor structure to the coupling block.
 19. The method of claim18, wherein the thermosetting adhesive is cured to bond thesemiconductor structure to the coupling block at a position ofessentially a maximum value of light intensity in the fiber by UVcuring.
 20. The method of claim 11, wherein the lens-grating is spacedby at least one-hundred wavelengths from the diffraction grating.